Oxidation process is a basic process for producing integrated circuits (IC) and manufacturing relevant products. In silicon technology, silicon dioxide is the first choice for local oxidation, trench isolation, and surface passivation because of its easy production, ready control, and excellent property. Moreover, the size of device elements gets smaller and smaller and it becomes more difficult to isolate a small element from others. The development of oxidation is very important to enter the filed of submicron. There are two major methods for forming silicon oxides based on different applications; one is dry thermal oxidation, and the other is wet thermal oxidation. The oxidizing rate by dry thermal oxidation is so slow that the method is only utilized for growing thin oxide layer. Thus, the growth of thick oxide layer used in trench isolation prefers wet thermal oxidation. These above methods based on silicon semiconductor have been adopted for a long time. Now, oxidation of gallium arsenide (GaAs) is concerned. GaAs offers several advantages such as higher speed, packing density, and wider bandgap, especially for processing the metal semiconductor field-effect transistor (MESFET). However, oxidation of GaAs is not processed easily and the available property is not good enough. For instance, the oxidizing rate of GaAs is very slow, e.g. less than 60 .ANG./hr, when the operating temperature is below 450.degree. C. If the operating temperature is higher, unstoichiometric oxide layer is formed because the difference of saturated vapor pressure between gallium oxide and arsenic oxide is great. The loss of arsenic oxide is more serious if the oxidation is carried out at temperature above 400.degree. C. Accordingly, the obtained oxide layer of GaAs has indefinite compositions. This trouble generally exists in oxidation of III-V compounds. The disadvantage of unhomogeneous composition is unfavorable to the application of III-V compound semiconductor having oxide layer structure such as metal-oxide semiconductor field-effect transistor (MOSFET). This is the reason that commercial integrated circuit based on III-V semiconductor is not used broadly.
By reviewing the prior references about the method for forming the oxide of III-V compounds, it is found that extensive research efforts have been done in the development of the oxidation of III-V compounds. In the previous studies, H.sub.2 O.sub.2 had been employed to oxidize AlGaAs and GaAs for surface passivation of junction lasers (U.S. Pat. Nos. 3,914,465 and 3,890,196). The other approaches require electrodes (U.S. Pat. Nos. 3,898,141, 3,859,178, and 3,929,589), condensed gas (Nandita Basu, et al., High-pressure thermal oxidation of n-GaAs in an atmosphere of oxygen and water vapor, J. Appl. Phys. 63(11), p5500-5506, 1988), energy sources like optical illumination (P. A. Bertrand, The photochemical oxidation of GaAs, J. Electrochem. Soc. 132(4), p973-976, 1985), laser beam (E. Ettedgui, et al., Photon-assisted oxidation of the GaAs (100) surface using water at 90 K, J. Appl. Phys. 77(10), p5411-5417, 1995), or excited plasma (U.S. Pat. No. 3,935,328 and Ryuichi Nakamura, et al., Magnetically excited plasma oxidation of GaAs, Jpn J. Appl. Phys., 35(1A), pL8-L11, 1996). The cost of essential equipments is great and the operating condition is trivial. An improved method is still needed to grow the oxide film of III-V compounds easily.
A method for forming a silicon oxide thin film in liquid phase and at lower temperature is developed (Hirotsugu Nagayama, et al., A new process for silica coating, J. Electrochem. Soc., 135(8), p2013-2016, 1988). The potentiality of this technology is noted recently because that the oxides produced by this method are homogenous. Besides, the condition of relatively low operating temperature is really attractive. Hence, in this specification, a new chemical-assisted oxidation method applied to GaAs in liquid phase near room temperature is disclosed. The oxide film provided by this method is homogenous, smooth, electric insulated, and chemical stoichiometric.